Machines for producing beverages, in particular beverages likely to degrade over time, such as milk-containing beverages, e.g. milk-containing coffee, tea or chocolate drinks are well known in the art.
As known in the art, in order to produce such a beverage, water may be passed via a heater for producing steam. The thus generated water steam can be fed to a mixing head in which, e.g. by applying a Venturi effect, milk supplied from a milk supply and air from an air inlet is sucked into the water steam flow which results in a heated water/milk mixture which can then be drained from an outlet nozzle of the mixing head into a cup.
A well known problem is that after having produced the desired amount of beverage, the parts of the machine that have been exposed to the beverage bear residues thereof, in particular milk, that may degrade or be unwantedly mixed with subsequently prepared beverages, in particular milk-free beverages, when the machine is suitable to prepare different types of beverages.
A typical example of such undesirable residue issues is encountered with in-line milk vapour-operated frothing or heating heads. The inlet of the head, the interior of the head itself as well as the outlet nozzle are exposed to milk and thus have to be cleaned to prevent contamination, e.g. by rinsing. In known devices, this is a labour intensive and time consuming work asking for a manual rinsing of the described milk flow path. The rinsing and/or cleaning can actually take substantially more time and effort than the step of producing the mixture. The cleaning is particularly difficult when the milk has dried on the surfaces of the mixing head. On the other hand, if the cleaning is not carried out properly and frequently enough, there can be hygiene-related problems in any subsequent use of the device.
A solution to this problem has been proposed in EP 1 656 863. A movable in-line venturi-based milk frothing head has a self-cleaning configuration in which the milk suction inlet is moved and dipped into a rinsing media and the milk outlet is moved over a collector for the used rinsing media. In this configuration, the rinsing media is driven through the head for cleaning thereof. The milk frothing head can be motorized to carry out the entire cleaning process automatically.
EP 1 374 748 discloses a venturi-type in-line frother which has: a milk inlet connected to a milk container; a water (steam) inlet connected to a water source; and an air inlet. The frother has a three-way valve to divert water or steam from the water source into the air inlet line and therefrom into the emulsification chamber for rinsing thereof. Simultaneously, steam is passed via the steam supply line into the steam inlet. The flushing water passed through the frother is collected in a waste basin. Consequently, milk traces are flushed out of the air and steam lines. The flushing process may be carried out at the end of each beverage preparation or at the user's request or automatically after some delay after a beverage preparation to avoid accidental scalding if a user inserts his or her hand beneath the beverage discharge duct immediately after beverage preparation.
Another approach involves the use of disposable parts that are exposed to the degradable liquid such as milk, for example as taught in EP 1 746 920.
There is still a need to provide a simple and hygienic cleaning arrangement for a beverage preparation machine.